This invention relates to an improved glue flap construction for a lined carton, and more particularly to a glue flap construction which does not leave any ingress or egress channels, thus, rendering the carton more completely sealed.
There exists a variety of container structures designed to store various perishables and air and water sensitive contents. These containers provide some degree of protection against the infiltration of moisture and vapor to the carton's contents. These containers may be of a type known in the art as a "pouch". The pouch is composed of material of uniform thickness. The pouch material may be sealed according to a method known in the art as "fin sealing". The fin sealed pouch is generally moisture and vapor proof because the face to face "fin" seal is of uniform thickness and is generally accomplished without leaving air channels.
Pouch containers as described above have the advantage of being moisture and vapor proof but have certain disadvantages. Pouches are generally made of materials that are soft and pliable and are therefore not self-supporting or crush-proof. Pouches are also more difficult to fill than stiff cartons in certain applications. In an attempt to overcome these problems and still maintain a moisture and vapor resistant container, containers have been developed in which a pouch is incorporated into a carton. These cartons are known in the art as "bag in a box".
In a modification of the "bag in a box" type container a lined carton may be made from a lined carton blank that is folded and sealed. Such lined cartons when made from a blank which includes a moisture and vapor resistant lining attached to carton stock have many advantages. These advantages include ease of storing, since the blanks may be stored flat until needed; ease of filling for certain applications; resistance to crushing, etc.
Such cartons may be formed from a lined carton blank which is scored to define panels and flaps and tabs. The panels and flaps and tabs are folded to form the sides and ends of the carton, respectively. The blank includes a glue flap on one side for folding under the inner surface of a panel on the opposite side of the blank. A rectangular heat sealable liner is adhered to the inner surface of the carton blank. The glue flap is attached to a rectangular side panel.
In such cartons, the glue flap has glue applied to its outside surface. A portion of the liner material is then folded over the glue flap. The glue flap and adhered liner are then adhered to the under surface of a side panel on the opposite side of the blank when the blank is folded into a carton. Such a partially constructed prior art carton with the carton lying flat is illustrated in a top view in FIG. 1.
The folded carton blank is noted generally as 10. The glue flap 12 has been folded under an opposite side panel 16 of the carton. A liner 17 is attached to the entire inside surface of the blank 10. The end panels of the carton are designated as 11 and 13 and the dust flaps as 15 and 19. The end edges of the glue flap are designated 14 and the side panel to which the glue flap is attached is designated as 21. The glue flap, the main body and the liner are normally caused to adhere to each other by application of heat and pressure.
A problem arises in the above described standard construction carton. Referring to FIG. 2, which is a cross-section of the glue flap and adjacent area taken along line 2--2, it has been found, that upon folding of the glue flap and adhesion of the glue flap to panel 16 an air channel 22 is left between the folded layers of liner 17. It is hypothesized that air channel 22 is left because of the abrupt thickness differential that exists between the components that are adhered together to the right and left of glue flap edge 14 as viewed in FIG. 2. The presence of this sharp thickness differential along edge 14 causes channel 22 to be left between the liner material partially covering the glue flap and the liner material covering that section of the opposite side panel which is adhered to the glue flap section. A second channel 24 is also left but it is of no consequence since it is a "dead end" channel that does not have access to the inside of the carton. The creation of air channel 22 provides a means for outside air or water vapor to infiltrate the container or means for the contents of the container to escape.
Infiltration of moisture vapor into a container may damage perishable, or vapor sensitive contents of the container. Air channels may also permit escape of fine materials stored in the container. A problem, therefore, exists in the construction of lined cartons according to the described prior art technique, because of the leaving of air channels in the carton resulting from the abrupt thickness differential between the liner-covered glue flap area and the thinner adjacent area.